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When a candle burns, why does the top of wick glow if bottom of flame is hottest?

4

1

$begingroup$

Totally an elementary question.

Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest.

Is the reason for this that the concentration of liquid wax is greater at the bottom, offsetting the greater temperature at the bottom?

thermodynamics heat combustion light

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edited 39 mins ago

A.K.

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asked 1 hour ago

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ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  The yellow part of a flame is coloured by glowing tar/char and wick particles.
  $endgroup$
  – Karl
  1 hour ago
  

  
  
  
  

add a comment | 

4

1

$begingroup$

Totally an elementary question.

Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest.

Is the reason for this that the concentration of liquid wax is greater at the bottom, offsetting the greater temperature at the bottom?

thermodynamics heat combustion light

share|improve this question

edited 39 mins ago

A.K.

10.2k62671

asked 1 hour ago

ZARZAR

1211

New contributor

ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  The yellow part of a flame is coloured by glowing tar/char and wick particles.
  $endgroup$
  – Karl
  1 hour ago
  

  
  
  
  

add a comment | 

$begingroup$

Totally an elementary question.

Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest.

Is the reason for this that the concentration of liquid wax is greater at the bottom, offsetting the greater temperature at the bottom?

thermodynamics heat combustion light

share|improve this question

edited 39 mins ago

A.K.

10.2k62671

asked 1 hour ago

ZARZAR

1211

New contributor

ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

share|improve this question

edited 39 mins ago

A.K.

10.2k62671

asked 1 hour ago

ZARZAR

1211

New contributor

ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 39 mins ago

A.K.

10.2k62671

asked 1 hour ago

ZARZAR

1211

New contributor

ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 39 mins ago

A.K.

10.2k62671

edited 39 mins ago

A.K.

10.2k62671

asked 1 hour ago

ZARZAR

1211

New contributor

ZAR is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 1 hour ago

ZARZAR

1211

2 Answers
2

active

oldest

votes

2

$begingroup$

Because fire is not the same thing as light.

Michael Faraday did a wonderful job of explaining how the candle works, and I direct to look at it (there are also Youtubes videos giving a modern take on this work) if you're interested.

In short, the candle produces light, not because it is hot, but because it is sooty. The particles of soot glow when they are hot (blackbody radiation), and that's what produces light.

If you take a flame where the fuel is very well-mixed with oxygen and the flame that's produced is not sooty, it does not glow like a candle even though it's very hot. This is precisely why Bunsen burners are used in a laboratory. They give a hot but non-illuminating flame that's great for doing analysis.

share|improve this answer

answered 1 hour ago

ZheZhe

13.2k12650

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I just browsed a bit in the Faraday lecture for children: wonderful!
  $endgroup$
  – Karsten Theis
  14 mins ago
  

  
  
  
  

add a comment | 

2

$begingroup$

The top of the wick glows because it is hotter than the bottom. The wick temperature does not have to be the same as the flame temperature.

For a candle, the wick burning isn't the intended purpose of the wick; light comes from burning wax (more generally: fuel), you want to burn the wax not the wick. Rather the purpose purpose of a wick is to help fuel evaporate by soaking up wax and allowing the radiant energy from the flame to heat the wax causing it to evaporate and burn also.

As wax travels up the wick, it evaporates and less wax is in the wick the further up you go. Eventually the dries up and the radiant energy is heating a wick without any wax. Eventually the wick get so hot at the tip, that it will glow due to black-body radiation.

In summary: though the blue is the hottest part of the flame, the wick can evaporate wax to cool towards the bottom. There is no wax at the top and thus as the radiant energy of the flame causes it to get hotter until it starts to glow.

Extra: I will note that the top of the wick does not burn when lit as the gas around the wick has too little oxygen to burn (unless the wick slumps out side the flame). When you blow out the candle the low oxygen environment of a flame is gone and thus the hot wick will smolder.

share|improve this answer

answered 37 mins ago

A.K.A.K.

10.2k62671

$endgroup$

add a comment | 

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2

$begingroup$

Because fire is not the same thing as light.

Michael Faraday did a wonderful job of explaining how the candle works, and I direct to look at it (there are also Youtubes videos giving a modern take on this work) if you're interested.

In short, the candle produces light, not because it is hot, but because it is sooty. The particles of soot glow when they are hot (blackbody radiation), and that's what produces light.

If you take a flame where the fuel is very well-mixed with oxygen and the flame that's produced is not sooty, it does not glow like a candle even though it's very hot. This is precisely why Bunsen burners are used in a laboratory. They give a hot but non-illuminating flame that's great for doing analysis.

share|improve this answer

answered 1 hour ago

ZheZhe

13.2k12650

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I just browsed a bit in the Faraday lecture for children: wonderful!
  $endgroup$
  – Karsten Theis
  14 mins ago
  

  
  
  
  

add a comment | 

2

$begingroup$

Because fire is not the same thing as light.

Michael Faraday did a wonderful job of explaining how the candle works, and I direct to look at it (there are also Youtubes videos giving a modern take on this work) if you're interested.

In short, the candle produces light, not because it is hot, but because it is sooty. The particles of soot glow when they are hot (blackbody radiation), and that's what produces light.

If you take a flame where the fuel is very well-mixed with oxygen and the flame that's produced is not sooty, it does not glow like a candle even though it's very hot. This is precisely why Bunsen burners are used in a laboratory. They give a hot but non-illuminating flame that's great for doing analysis.

share|improve this answer

answered 1 hour ago

ZheZhe

13.2k12650

$endgroup$

• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I just browsed a bit in the Faraday lecture for children: wonderful!
  $endgroup$
  – Karsten Theis
  14 mins ago
  

  
  
  
  

add a comment | 

$begingroup$

Because fire is not the same thing as light.

Michael Faraday did a wonderful job of explaining how the candle works, and I direct to look at it (there are also Youtubes videos giving a modern take on this work) if you're interested.

In short, the candle produces light, not because it is hot, but because it is sooty. The particles of soot glow when they are hot (blackbody radiation), and that's what produces light.

If you take a flame where the fuel is very well-mixed with oxygen and the flame that's produced is not sooty, it does not glow like a candle even though it's very hot. This is precisely why Bunsen burners are used in a laboratory. They give a hot but non-illuminating flame that's great for doing analysis.

share|improve this answer

answered 1 hour ago

ZheZhe

13.2k12650

$endgroup$

share|improve this answer

answered 1 hour ago

ZheZhe

13.2k12650

answered 1 hour ago

ZheZhe

13.2k12650

answered 1 hour ago

ZheZhe

13.2k12650

2

$begingroup$

The top of the wick glows because it is hotter than the bottom. The wick temperature does not have to be the same as the flame temperature.

For a candle, the wick burning isn't the intended purpose of the wick; light comes from burning wax (more generally: fuel), you want to burn the wax not the wick. Rather the purpose purpose of a wick is to help fuel evaporate by soaking up wax and allowing the radiant energy from the flame to heat the wax causing it to evaporate and burn also.

As wax travels up the wick, it evaporates and less wax is in the wick the further up you go. Eventually the dries up and the radiant energy is heating a wick without any wax. Eventually the wick get so hot at the tip, that it will glow due to black-body radiation.

In summary: though the blue is the hottest part of the flame, the wick can evaporate wax to cool towards the bottom. There is no wax at the top and thus as the radiant energy of the flame causes it to get hotter until it starts to glow.

Extra: I will note that the top of the wick does not burn when lit as the gas around the wick has too little oxygen to burn (unless the wick slumps out side the flame). When you blow out the candle the low oxygen environment of a flame is gone and thus the hot wick will smolder.

share|improve this answer

answered 37 mins ago

A.K.A.K.

10.2k62671

$endgroup$

add a comment | 

2

$begingroup$

The top of the wick glows because it is hotter than the bottom. The wick temperature does not have to be the same as the flame temperature.

For a candle, the wick burning isn't the intended purpose of the wick; light comes from burning wax (more generally: fuel), you want to burn the wax not the wick. Rather the purpose purpose of a wick is to help fuel evaporate by soaking up wax and allowing the radiant energy from the flame to heat the wax causing it to evaporate and burn also.

As wax travels up the wick, it evaporates and less wax is in the wick the further up you go. Eventually the dries up and the radiant energy is heating a wick without any wax. Eventually the wick get so hot at the tip, that it will glow due to black-body radiation.

In summary: though the blue is the hottest part of the flame, the wick can evaporate wax to cool towards the bottom. There is no wax at the top and thus as the radiant energy of the flame causes it to get hotter until it starts to glow.

Extra: I will note that the top of the wick does not burn when lit as the gas around the wick has too little oxygen to burn (unless the wick slumps out side the flame). When you blow out the candle the low oxygen environment of a flame is gone and thus the hot wick will smolder.

share|improve this answer

answered 37 mins ago

A.K.A.K.

10.2k62671

$endgroup$

add a comment | 

$begingroup$

The top of the wick glows because it is hotter than the bottom. The wick temperature does not have to be the same as the flame temperature.

For a candle, the wick burning isn't the intended purpose of the wick; light comes from burning wax (more generally: fuel), you want to burn the wax not the wick. Rather the purpose purpose of a wick is to help fuel evaporate by soaking up wax and allowing the radiant energy from the flame to heat the wax causing it to evaporate and burn also.

As wax travels up the wick, it evaporates and less wax is in the wick the further up you go. Eventually the dries up and the radiant energy is heating a wick without any wax. Eventually the wick get so hot at the tip, that it will glow due to black-body radiation.

In summary: though the blue is the hottest part of the flame, the wick can evaporate wax to cool towards the bottom. There is no wax at the top and thus as the radiant energy of the flame causes it to get hotter until it starts to glow.

Extra: I will note that the top of the wick does not burn when lit as the gas around the wick has too little oxygen to burn (unless the wick slumps out side the flame). When you blow out the candle the low oxygen environment of a flame is gone and thus the hot wick will smolder.

share|improve this answer

answered 37 mins ago

A.K.A.K.

10.2k62671

$endgroup$

share|improve this answer

answered 37 mins ago

A.K.A.K.

10.2k62671

answered 37 mins ago

A.K.A.K.

10.2k62671

answered 37 mins ago

A.K.A.K.

10.2k62671